I am sorry to say that Amtrak is behind the rest of the rail world in dealing with bikes. On most trains bikes must be boxed and put on as checked baggage. Amtrak only deals with checked baggage at the big stations like Atlanta. Anniston is just a flag stop, no checked baggage on or off. There are a few trains in the Northeast and CA that have bike racks in each car to hang a few bikes. They should all be that way, but are not. I suggest you write to Amtrak and suggest they put racks on all their train. They will do it if lots of people chime in.
My suggested alternative is to do a round trip. Park at the AL end and ride to Smyrna. If you can stay at Dobbins you can probably get there on a Cobb County Transit bus, which do have bike racks. Ride back the next day. If you are uncomfortable with back to back centuries you could take two days to return if you have a three day weekend. Cedartown sits about halfway on the route and has reasonable motels and restaurants.
Also, out and backs are really not so bad. The scenery looks different going back. It is just so nice to be out of traffic.
My plans are to do a four day round trip from the GA end, staying in Cedartown twice and a motel near Jackonsville State. Four 50 mile days would be pleasant for the level of riding I do.